Alkyl--alkyl ethers (R--O--R) such as methyl t-butyl ether (hereinafter "MTBE") are being used as octane-enhancers in the reformulation of low volatility unleaded gasoline blends and for reducing the emission of volatile organic compounds from engines. In general, alkylethers, especially those alkylethers which have only one ether linkage and without other functional groups, are chemically stable compounds and there is little information on their biodegradability in soil, groundwater and activated sludge environments. The lack of alkylether degradation by indigenous microbes in soils and biosludges may be attributed to the very stable and chemically unreactive ether linkage, the inability of these compounds to be transported into cells and/or the lack of inducible or existing enzyme activities (e.g. oxygenases, hydroxylases) which can attack the ether bond.
It is known that MTBE can persist in groundwater from accidental spills of unleaded gasoline from underground storage tanks. However, no known naturally-occurring microbial cultures exist to effectively biotreat groundwater, wastewater, tank bottom wastes or soils containing this ether.
Alkyl ethers such as symmetric dioctyl ether have been shown by Modrzakowski and Finnerty to be only partially oxidized by an Acinetobacter strain in which the ether linkage is not cleaved and only the terminal carbons are utilized for growth. See, Intermediary Metabolism of Acinetobacter Grown on Dialkyethers. Can. J. Microbiol., 35:1031-1036 (1989).
Studies on the biodegradability testing of MTBE in sludges and soils by Fujiwara et al. showed that 100 ppm MTBE or diisopropylether (DIPE) does not degrade in activated sludge (300 ppm solids) in an oxygen uptake assay. Moreover, MTBE did not significantly affect the respiration rate of other hydrocarbons when blended (12% w/v) with the fuel. See, Fujiwara, T., T. Kinoshita, H. Sato and I. Kojima, Biodegradation And Bioconcentration of Alkyl Ethers, Yukagaku 33: 111-114 (1984).
Moller and Arvin proposed that MTBE (10 ppm) or TAME (t-amyl methyl ether, 3 ppm) were not degraded in 60 days by microbes in an aquifer soil, topsoil or activated sludges. In these experiments, MTBE at 200 ppm levels showed a weak inhibitory effect on the biodegradation of aromatic hydrocarbons (3.5 ppm BTEX). See, Moller, H. and E. Arvin, Solubility and Degradability of The Gasoline Additive MTBE, Methyl-tert-butyl-ether and Gasoline Compounds in Water, Contaminated Soil '90, 445-448 (1990), Kluwer Academic Publishers.
Recent studies by Suflita and Mormile on the anaerobic degradation of gasoline oxygenates in a landfill aquifer material showed that of several alkyl ethers tested (MTBE, TAME, ETBE, DIPE, ethyl ether, propyl ether) only n-butyl methyl ether was metabolized under anaerobic methanogenic conditions. MTBE is only cleaved under anaerobic condition to t-butyl alcohol which is not degraded further. See Suflita, J. M. and M. R. Mormile, Anaerobic Biodegradation of Known and Potential Gasoline Oxygenates in the Terrestrial Subsurface, Environ. Sci. Technology 27: 976-978 (1993).
Parales et al isolated an actinomycete from biosludge which was shown to grow on 1,4-dioxane could also utilize some of the linear alkyl ethers such as diethyl ether and methyl butyl ether, but not the branched alkyl ethers such as diisopropylether, ethyl t-butyl ether or ethylene glycol ethers. See, Parales, R. E., J. E. Admus, N. White, H.D. Degradation of 1,4-dioxane by an Actinomycete in Pure Culture, Applied Environ Microbiol, 60, 4527-4530, May, 1994.
Japanese patent application number 04,110,098, filed by Kyowa Hakko Kagyo KK, proposes the decomposition of ethylene glycol alkylethers with bacteria. The ethers decomposed have more than one ether linkages and/or have hydroxyl functional groups, which are known to be more readily degradable than those with only one ether linkage and without other functional groups.
Japanese patent application number 62,208,289, filed by Hodogaya Chem. Ind. KK, proposes the degradation of polyoxytetramethylene glycol with bacterial strains. The ethers degraded have multiple ether linkages and thus are more readily degradable than those with only one ether linkage and with no other functional groups.
Thus, there remains a need for a bacterial culture capable of degrading under aerobic condition an ether, especially an alkyl ether, more especially a branched alkyl ether such as MTBE. The culture would be useful for treating wastes and groundwater containing ethers, especially branched alkyl ethers such as MTBE.